barack obama will be preparing for debates in nevada, where cbs expects 65% of vote voters to vote early. his presence in the state of nevada stirs up activities for democrats who then will try to arck up their voters early. if a campaign can get lots of voters to vote early, then the campaign can spend its time and resources in other battleground states with other voters. >> pelley: these early votes aren't counted until election day. i wonder how do the campaigns know how people are voting early? >> the secretary of state in most of the early voting states hports daily the names of those who voted-- not how they voted, just that they did. what the campaigns then do is match that against the lists of voters they've identified over the years. so if mrs. jones has asked for an early ballot but isn't on that daily report, the campaign will contact her. this is why ground game matters. they often know what mrs. jones ndres about, and that's what they'll talk about when they call her to push her to vote. operatives from both parties joke that with voters will the best way to stop the calls,